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Dual Focussed Induction / Ultra-slim Induction

The dual focussed induction probe provides two simultaneous conductivity logs, corresponding to “medium” and “deep” radii of investigation into the formation. The two depths of penetration are useful in porous, permeable formations where displacement of formation fluids by drilling mud creates an “invasion zone” with different electrical properties. The 1” focussed induction probe produces a single medium penetration conductivity log. It finds particular application in small-diameter dry or plastic-lined boreholes used for mineral exploration.

Principle of Measurement:

An oscillating high-frequency magnetic field from a transmitter coil within the probe induces an alternating electrical current within the surrounding conductive formation. This current, in turn, induces voltages within receiver coils proportional to the formation conductivity. The transmitter-receiver spacings determine the depth of investigation of the measurements. Additional focussing coils minimise the contribution of the borehole signal.


  • Formation conductivity measurement in wet/dry boreholes or through plastic casing
  • Separate deep and medium penetrating measurements give information on invaded zone
  • Focussed measurements for minimum borehole signal PSD (phase-sensitive detector) discriminates between magnetic susceptibility and conductivity signals


  • Deep formation conductivity
  • Shallow formation conductivity
  • Medium formation conductivity
  • Natural gamma



  • Indicator of permeable zones and porosity
  • Formation water salinity
  • Long-term well monitoring


  • Ore identification and quality
  • Correlation


  • Indication of hydrocarbons


Diameter 38mm/ 25mm
Length: 2.32m/ 1.95m
Weight: 8kg
Temperature: 0-70⁰C (extended ranges available)
Max. pressure: 20MPa
Number of coils: Dual Induction 7, Ultra-slim 4
TX-RX spacings: ILM 50cm (20”); ILD 81cm (32”)
Conductivity range: 200 to 10,000mS/m

Operating Conditions

  • Borehole type: open/plastic or grp cased, air/water-filled fin stand-off recommended

Sales Information

I002087 Dual focussed induction probe with natural gamma
I002091 Ultra-slim induction probe with natural gamma

Download Dual Focussed Induction / Ultra-slim Induction sheet


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Robertson Geologging Ltd., 2017

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